We have good crystals of calmodulin, S-100 and crayfish sarcoplasmic calcium binding protein (CSCBP). We have recorded and processed a 4.5 A resolution sphere of calmodulin X-ray diffraction data, and 3.0 A sets from S-100 and CSCBP. We propose to solve, refine, and analyze these three crystal structures. Concurrently we will be doing the preparatory biochemistry and crystallization work to start new structure determinations for other calcium modulated and calcium binding proteins. We have received samples of highly purified aequorin and osteocalcin and have defined precipitation conditions. We intend to grow usable crystals of osteocalcin and of aequorin. Knowing the crystal structure of calmodulin is only the beginning of the study of its chemistry. We will try to grow crystals of it complexed with one of its targets. Troponin-I, myosin light chain kinase and the gamma subunit of phosphorylase kinase are the most promising.